It is known from the prior art that clean wax products, ie wax products containing less than 50 mass ppm total cobalt, can be obtained during slurry phase Fischer-Tropsch synthesis involving contacting a synthesis gas comprising hydrogen and carbon monoxide at elevated temperature and pressure with a particulate supported cobalt Fischer-Tropsch synthesis catalyst, to produce the clean wax products. The clean wax product can be defined as being the filtrate of the liquid Fischer-Tropsch synthesis product (ie reactor wax) continuously extracted directly from the reactor slurry phase through an in-situ primary filtration process. The particulate supported cobalt slurry phase Fischer-Tropsch synthesis catalysts are sufficiently strong so that little break-up thereof during extended slurry phase Fischer-Tropsch synthesis runs takes place, and cobalt crystallites are sufficiently anchored to the catalyst support to prevent cobalt from readily dislodging and washing out of the cobalt catalyst during such extended slurry phase Fischer-Tropsch synthesis runs conducted at realistic conditions, also implying catalyst stability in the associated hydrothermal environment.
This objective is successfully achieved in the prior art through the introduction, during production of a catalyst precursor from which the catalyst is obtained, of additional processing step(s) to modify an already pre-shaped catalyst support, such as Al2O3, MgO or TiO2, thus producing a modified catalyst support, wherein the cobalt crystallites are sufficiently anchored to the selected catalyst support to prevent cobalt from readily dislodging and washing out of the resultant cobalt catalyst during the extended slurry phase Fischer-Tropsch synthesis runs. Such a catalyst is preferably prepared through the aqueous phase impregnation of the modified catalyst support with cobalt.